NUTRIENTS

AND FLORIDA’S

COASTAL WATERS

NUTRIENTS

AND FLORIDA’S

COASTAL WATERS

by

Jennifer Hauxwell

Charles Jacoby

Thomas K. Frazer

John Stevely

SGEB-55

THE LINKS BETWEEN PEOPLE,

INCREASED NUTRIENTS AND

CHANGES TO COASTAL AQUATIC SYSTEMS
Acknowledgments

We thank Bill Seaman for initiating this effort, and

Dorothy Zimmerman and Steve Kearl for guiding

it through the editorial process. Kenneth Louis

Clark waded through our suggestions and expertly

prepared the illustrations. Regina Cheong dealt with

the layout cheerfully, efficiently, and effectively.

The Authors

Jennifer Hauxwell

Department of Natural Resources Research Center

Wisconsin Department of Natural Resources

1350 Femrite Drive

Monona, Wisconsin 53716

Charles Jacoby

Department of Fisheries and Aquatic Sciences

University of Florida

7922 NW 71st Street

Gainesville, Florida 32653-3071

Thomas K. Frazer

Department of Fisheries and Aquatic Sciences

University of Florida

7922 NW 71st Street

Gainesville, Florida 32653-3071

John Stevely

Florida Sea Grant Extension Program

1303 17th Street West

Palmetto, Florida 34221-5998

This publication was supported by the National

Sea Grant College Program of the U.S. Department

of Commerce’s National Oceanic and Atmospheric

Administration (NOAA) under NOAA Grant No.

76 RG-0120, and by the UF/IFAS Center for

Natural Resources. The views expressed are those of

the authors and do not necessarily reflect the views

of these organizations.

Additional copies are available by contacting

Florida Sea Grant, University of Florida, 

PO Box 110409, Gainesville, FL, 32611-0409, 

(352) 392-5870.

Cover photo: Aerial of North Fork of the St. Lucie

River. Photo courtesy of South Florida Water

Management District.

NUTRIENTS AND FLORIDA’S COASTAL WATERS: THE

LINKS BETWEEN PEOPLE, INCREASED NUTRIENTS,

AND CHANGES TO COASTAL AQUATIC SYSTEMS

All of us benefit from healthy coastal ecosystems. If we want our

recreational, commercial and other social benefits to continue, we have a

responsibility to protect the health of these systems. Balancing protection

and use of coastal systems creates some difficult decisions.

Florida Sea Grant recognizes the importance and complexity of such

decisions. As part of its efforts to enhance the practical use and conservation

of coastal and marine resources, it contributes to informed debate by

producing and distributing objective, valuable, and understandable

information. In order to produce such information, Florida Sea Grant

works with scientists from many collaborating organizations.

This brochure represents one of Florida Sea Grant’s efforts to generate

understanding and debate. In collaboration with researchers from the

University of Florida, we introduce an important and complex topic:

how nutrients function in coastal aquatic systems and how human activities

affect these natural cycles. Although a full explanation of nutrient

dynamics is beyond the scope of this brochure, it does help us understand

and manage these important phenomena.

Florida Sea Grant also recognizes that the issues related to use and

protection of Florida’s coast extend beyond nutrients in coastal waters.

For that reason, it is producing other documents to accompany this one.

For example, Submarine Groundwater Discharge: An Unseen Yet Potentially

Important Coastal Phenomenon (SGEB-54), has been released. A citizen’s

guide to Florida’s estuaries is in preparation.

We ask that you read this material and pursue some of the additional

information. We also ask that you contact us with questions or comments.

Florida Sea Grant’s ability to achieve its objectives and our collective ability

to ensure sustainable use of coastal systems depend, in large part, on your

involvement and input.

Thank you for your time and interest.

Charles Jacoby

Extension Specialist, Estuarine Ecology

Leader, Florida Sea Grant Coastal Environmental and 

Water Quality Design Team
Coastal aquatic systems, including estuarine and marine

nearshore environments, deserve our attention for

three key reasons. First, healthy coastal systems provide

homes and food for numerous plants and animals. Second,

we use these systems extensively for commercial and

recreational activities, and third, both our coastal and

inland activities can pose threats to the health of coastal

aquatic systems.

One of the primary ways we threaten the health of

coastal systems is through addition of nutrients. Nutrients

occur naturally, and they support natural processes that

make coastal systems unique. Unfortunately, our activities

can increase nutrients to levels that cause undesirable

changes. One of the most important ways we affect coastal

waters is through activities on land that increase delivery of

nutrients

to the sea.

This booklet 

provides information

about the links between nutrients and the health of

Florida’s coastal ecosystems. It uses definitions, conceptual

models, and summaries of current knowledge to explain

how coastal ecosystems function under natural conditions

and how people are increasingly affecting coastal ecosystems.

Sources of more information and suggestions for ways to help

protect our precious coastal systems are included. Through a

greater understanding of coastal systems, nutrients, and how

people affect natural processes, each of us can make

informed choices that reduce environmental damage.

COASTAL SYSTEMS AND NUTRIENTS...

EXACTLY WHAT ARE WE TALKING ABOUT?

Coastal systems include the water, bacteria, plants, and

animals found in bays, lagoons, estuaries, and

nearshore areas. All living things in coastal systems are

connected as illustrated by a food web (Figure 1). At the

base of coastal food webs, primary producers

(including seagrass, algae,

Figure 1: Simplified food web with connections among trophic levels. Primary producers (bacteria, phytoplankton, algae, and 

seagrass) produce organic matter through photosynthesis. Primary consumers feed directly on bacteria and plants. 

Secondary consumers eat primary consumers, and, in turn, are eaten by tertiary consumers. In truth, trophic connections 

are often much more complex, with consumers feeding at several trophic levels. (Source: Florida Sea Grant)
and some species of bacteria) capture nutrients, sunlight,

and carbon dioxide (CO2) and use them to build new tissue

and release oxygen (O2) as a byproduct through a process

called photosynthesis. The production of new tissue is

referred to as primary production. Consumers, like us, feed

on primary producers or other consumers to gain energy

for survival, growth, and reproduction. All living things,

including primary producers, generate energy by consuming

organic material through a process called respiration. In

most cases, O2 is used during the breakdown of organic

matter and release of stored energy.

In coastal systems, as in many other ecosystems, 

primary production is often limited by the availability of

nutrients. Nutrients are chemical elements that influence

the productivity of all natural systems. Some elements that

are essential for the survival of primary producers and

consumers include nitrogen, phosphorus, potassium,

calcium, magnesium, sulfur, iron, manganese, copper,

zinc, molybdenum, sodium, cobalt, chlorine, bromine,

silicon, boron, and iodine. Primary producers extract these

essential nutrients directly from the environment. Like all

consumers, we get most of these elements from the food we

eat. In other words, we draw our nutrients from a food web.

Inputs of nutrients and other materials from the land

are a key feature distinguishing coastal systems from the

offshore oceanic environment. Although the exact offshore

boundary of a coastal system is difficult to pinpoint, we

can think of it as the place where inputs from the land no

longer have a significant influence. Inputs from the land

support rapid growth and reproduction of primary producers

and consumers making these areas among the most highly

productive in the world. Research shows that although

coastal waters represent only 10 percent of the total ocean

surface, they account for 20 percent of total primary

production and 50 percent of total fish production in the

oceans.3 In large part, production of fish is high because of

the food and shelter provided by primary producers in these

relatively nutrient-rich waters (see shaded box, this page).

HOW ARE COASTAL SYSTEMS

THREATENED?

Coastal systems in Florida are affected both directly

and indirectly by many human activities. For example,

two key intertidal coastal habitats, mangroves and salt

marshes, have often been destroyed to make way for

housing and other developments. In Florida, dredging and

filling operations have destroyed over 23,000 acres out of

the state's 469,000 acres of mangroves.4,5 In addition,

Florida's coastal reefs have been damaged by direct contact

from boaters and divers, as well as through the indirect

effects arising from nutrient additions these systems.

Direct damage to coastal habitats is something to be

avoided, but in many areas, indirect effects from human

activities are more threatening.

In Florida and other places around the world, seagrass

meadows represent one of the most disturbed coastal habitats

and provide a good example of both direct and indirect

effects of human activity on habitat.

HOW DO PEOPLE THREATEN SEAGRASS

MEADOWS?

Under natural conditions, seagrasses often represent a

major submerged aquatic habitat (see shaded box,

page 3). Seagrass habitat has been lost from waters off

Florida, as well as from coastal waters around the world,

due to natural and human-induced disturbances.

2

MEASURING THE IMPORTANCE OF

FLORIDA COASTAL SYSTEMS

Florida’s coastal environments represent one of the

state’s most distinctive and prominent features.

Maintaining the health of these environments is crucial.

Not only do they support fisheries, recreational activities,

and tourism, but they also provide the quality of life

that Floridians have come to enjoy. Did you know that

coastal environments:

• border 35 of Florida’s 67 counties;

• extend for 1,350 miles, which is longer than the 

Atlantic coast from Georgia through Maine;

• contain many habitats including coral reefs, sea

grasses, mangroves and wetlands;

• shelter, during some part of their lives, grouper, sea

trout, redfish, oysters, clams, scallops, blue crabs, 

lobsters, and other animals adding up to over 

80 percent of the animals caught by recreational 

and commercial fishers;

• house 60 percent of Florida’s 16 million residents 

within a band 10 miles wide;

• draw 10 million tourists each year (twice the 

number visiting inland parks)1;

• support beach tourism, which generates 

approximately $15 billion annually2; and 

• support marine fisheries worth $10 billion per year?
Natural disturbances that directly damage seagrasses

include hurricanes, earthquakes, ice scour, animals digging

through the substrate, animal grazing, and disease.

However, these pressures account for less than 20 percent

of the worldwide loss of seagrasses.6

Human activities also damage seagrass directly.

Dredging, construction of docks, mooring of boats,

harvesting of shellfish with rakes or trawls, and use of

motorboats in shallow waters all physically remove seagrass

meadows and created “scarred” areas. Seagrass meadows

with scars often suffer erosion and further loss of seagrass

during storms. In some meadows, scarring is a significant

problem, and overall approximately 6 percent of Florida's

seagrass meadows are scarred.7

In general, though, the links between many human

activities and effects on seagrasses involve multiple steps.

These effects are classed as indirect simply because

materials first need to be transported to the coast. One

example is herbicides carried to coastal waters, which can

then poison seagrasses. Another is sediment transported from

cleared land to coastal water, which can indirectly damage

seagrass by blocking out the light that it needs to grow.8

But it is the indirect effects of excess nutrient loading from

watersheds to coastal waters that are cited as the most

pervasive human impacts on coastal areas and on seagrass

habitat. 7,8,9-14 Around the world, increased nutrient

loading has accounted for 50 percent of the recorded

declines in seagrass, and this problem is growing.6

WHAT HAPPENS TO SEAGRASSES WHEN

TOO MANY NUTRIENTS REACH COASTAL

SYSTEMS?

Algal blooms are one common result of excess nutrients

being delivered to coastal waters. Algae differ from

seagrasses and terrestrial plants in that they lack vascular

structures such as roots and stems. Algae may be microscopic,

such as single-celled phytoplankton, or easily seen by the

naked eye, macroscopic, and they may be free-living or

attached. Many species of algae have lower light requirements

than seagrasses, so algal growth is typically limited by the

availability of nutrients.

In Florida and many other places around the world,

undesirable increases in both small and large algae have

become more common due to increased nutrient loading

to coastal waters. Increased numbers of microalgae, or

phytoplankton, often give the water an opaque, greenish

appearance. Increased quantities of macroalgae may result

in piles of rotting “seaweed” on the bottom in coastal waters

or on beaches. Such undesirable increases in algae indicate

that the system is undergoing human-induced eutrophication,

or an unnaturally rapid buildup of organic matter.

Increased amounts of phytoplankton or macroalgae

may indirectly lead to the loss of seagrass (Figure 2).10, 12, 14

Increased nutrients in the water column have little direct

effect on seagrass growth because seagrass roots generally

absorb all the nutrients they need from within the sediment.

In contrast, fast-growing phytoplankton, algae that grow

on seagrass (epiphytes), and algae that grow on the bottom

3

WHAT ARE SEAGRASSES?

Although they grow underwater, seagrasses are related

to flowering land plants, or angiosperms. Two key

characteristics that qualify seagrasses as angiosperms are:

1) a system of tubes, called a vascular system, which

transfers material within the plant, and 2) the production

of flowers as a way to reproduce sexually. Like many

land plants, seagrasses also reproduce vegetatively, with

new clones branching from an established plant.

As a result of both sexual and vegetative reproduction,

seagrasses often form extensive meadows. Along the

coasts of Florida, seagrass meadows cover more than 

2.7 million acres.6These meadows serve several important

ecological roles, including:

1) fixing carbon dioxide (CO2) into new plant tissue

at twice the rate achieved by highly cultivated 

crops, such as corn or rice. (Some seagrasses can 

produce more than 800 grams of carbon per 

square meter per year.);

2) providing food or shelter for thousands of marine 

organisms (including invertebrates, fish, water

fowl, sea turtles, and manatees); and

3) preventing coastal erosion by binding sediments 

with below-ground root and rhizome systems and 

by reducing wave energy or the speed of currents 

with above-ground leaf material.

In Florida, several seagrass species thrive in coastal 

shallow waters, including:

1) Thalassia testudinum (turtle grass);

2) Halodule wrightii (shoal grass);

3) Syringodium filiforme (manatee grass);

4) Halophila engelmannii (star grass);

5) Halophila johnsonii (Johnson’s seagrass);

6) Halophila decipiens (paddle grass); and

7) Ruppia maritima (widgeon grass).
affect not only the habitat and food available to animals

but also the “biogeochemistry” of coastal waters (see box

on this page, for an example). Under normal, low nutrient

conditions, O2 concentrations rise during the day as primary

producers photosynthesize and produce O2 and fall during

the night as all organisms respire or use O2 to generate

energy. Generally, O2 concentrations remain high enough

for animals to survive. However, excessively low O2

conditions arise when respiratory use of O2 by aquatic

communities (primary producers and consumers) exceeds

the sum of O2 release during photosynthesis by primary

producers and passive diffusion of O2 from air to water.

Under such circumstances, certain invertebrates and fishes

may suffocate.

In particular, increased amounts of algae caused by

increased nutrient loading can cause O2 concentrations to

(benthic macroalgae) are often nutrient limited, and they

respond to higher nutrient loads by growing faster.12, 14,

15–18 Increased amounts of these producers remove a large

percentage of the light that would otherwise have been

available for seagrass photosynthesis, and the seagrasses are

“starved” of the light they need to survive. Lack of suitable

light, in fact, is probably the major cause of damage to

seagrasses. This “shading” effect can also damage habitats

other than seagrass. For example, overgrowth of algae

leading to reduced light can eventually kill corals.

The indirect effects of increased nutrients do not stop

at the loss of seagrass habitat because that loss often means

that an important habitat for some animals is degraded. As

seagrasses are lost, animal numbers may decline because

they rely on seagrass for protection from predators or

because they rely on plants and animals in seagrass meadows

for food. Examples of animals affected in this manner

include certain species of invertebrates (such as amphipods,

isopods, shrimps, and snails) that are important in the diet

of several species of fishes. Furthermore, juvenile scallops

often settle directly upon the leaves of seagrasses, and the

loss of seagrass may contribute to diminished numbers of

scallops along Florida’s Gulf coast. For a few species,

increased primary productivity may actually represent an

increase in food. For example, growth rates of clams like

the quahog, Mercenaria mercenaria, may increase in systems

with higher nutrient loads because extra nutrients stimulate

production of their food – phytoplankton and particles

that are filtered from the water column.19

The shift from seagrass to a system with more algae

and more organic matter (a more eutrophic system) can

4

HOW CAN BIOGEOCHEMICAL CHANGES

AFFECT COASTAL SYSTEMS?

High concentrations of nutrients, particularly nitrogen,

carried by the Mississippi River to the Gulf of Mexico

have stimulated substantial increases in algal production.

Much of the excess algae settles to the seafloor where it is

degraded by bacteria. The degradation process consumes

O2, and greater inputs of algae cause more degradation and

more loss of O2. Extensive loss of oxygen, a biogeochemical

change, creates a “dead zone” in the northern Gulf of

Mexico.20–22 In essence, the “dead zone” contains no living plants or animals. During the past 20 summers, the

dead zone has increased in size to cover an area the size

of New Jersey.

A B

Figure 2: Drawings of a) a healthy seagrass bed and b) an unhealthy seagrass bed shaded and overgrown by phytoplankton and algae as a 

consequence of increased nutrients. (Source: Florida Sea Grant)
most abundant chemical element in living tissue, behind

oxygen, carbon, and hydrogen. Phosphorus is also a key

component in DNA, and it is found in adenosine

triphosphate (ATP), a molecule that is important in energy

transfer and storage in living cells.

Because N and P largely control primary productivity,

we are primarily concerned about their addition to our

coastal waters. Phosphorus is often the “limiting”

nutrient in freshwater environments, meaning the 

addition of P stimulates primary productivity. Nitrogen

is more frequently limiting in marine environments.

However, many exceptions to this pattern can be found

along the coast of Florida and elsewhere around the

world. Some of Florida’s coast has sediments that are

rich in calcium carbonate (CaCO3). Phosphate (PO4),

the form of P typically used by primary producers,

binds to these sediments and becomes less available. So,

in Florida’s coastal waters, either N or P may limit

growth. We focus here on N as an example of how

humans affect the natural cycles of key nutrients.

fluctuate greatly. Although algae contribute O2 when they

photosynthesize, their respiration and the respiration of

bacteria that degrade dead algae can use more O2 than is

produced. On sunny days, photosynthetic production is

usually greater than respiratory demand and there may be

no problem. However, a series of cloudy days can lead to

less photosynthesis and less O2 production, so that respiratory demand can exceed O2 availability. In these situations,

low oxygen concentrations (hypoxia) or loss of all oxygen

(anoxia) causes the death of invertebrates and fishes.

WHAT NUTRIENTS ARE WE CONCERNED

ABOUT AND WHY?

Of all the essential nutrients, nitrogen (N) andphosphorus (P) are the two nutrients that most often

limit the growth of primary producers. Nitrogen is a key

component in 1) chlorophyll, the green pigment in primary

producers that absorbs sunlight during photosynthesis,

2) amino acids, the building blocks of proteins, and

3) genetic material, including deoxyribonucleic acid (DNA)

and ribonucleic acid (RNA). Nitrogen ranks as the fourth

5

Figure 3: Simplified diagram of the nitrogen cycle showing some key sources of nitrogen (household septic systems; fertilizer from lawns,

gardens and agriculture; waste from livestock; point source discharges from wastewater treatment plants and industry; exhaust from 

cars; and emissions from industry), some key mechanisms that transport nitrogen (rain, runoff, leaching, groundwater, and rivers),

and some key processes that transform nitrogen (nitrogen fixation, denitrification and photosynthesis). (Source: Florida Sea Grant)
HOW DO PLANTS AND ALGAE GET

NITROGEN?

Many essential nutrients are made available to primary

producers through natural weathering of the earth’s

crust. Unlike other nutrients, N is most abundant as dinitrogen gas (N2). In fact, this gas comprises 78 percent of

the air we breathe. Although it is abundant, N still limits

the growth of primary producers, because most plants and

algae cannot directly use N2. Primary producers cannot

break the very strong and stable chemical bonds between

the atoms in nitrogen gas.

So, how do primary producers get N (Figure 3)?

Lightning can produce the immense, focused energy needed

to break the bonds in N2, and it produces nitrite (NO2),

nitrate (NO3), and ammonia (NH3). In addition, living

organisms called nitrogen-fixers can convert N2 to

ammonium (NH4), the form of N most readily taken up by

primary producers. In terrestrial environments, free-living

microbes and symbiotic bacteria in peas, alfalfa, soybeans

and other legumes perform this function, and in marine

environments, cyanobacteria (commonly called blue-greens)

fix N. Plants can also take up NO3, but this process requires

energy (the use of ATP), and NO3 must be converted to

NH4 before the N can be used in protein synthesis. Other

natural sources of N are the production of animal waste,

natural burning of organic matter or fossil fuels, and the

decomposition of organic material, such as the decay of

dead algae.

HOW DO PEOPLE AFFECT SUPPLIES OF

NITROGEN TO COASTAL WATERS?

There are three primary sources of human-derived N:

1) wastewater, 2) fertilizer, and 3) atmospheric pollution

(Figure 3). Nitrogen from these sources is delivered to

coastal regions in three ways: 1) point source inputs of

water, such as rivers or wastewater outlets; 2) nonpoint

source inputs of water, such as direct surface runoff or

groundwater that has percolated through the soil, into an

aquifer and out to coastal waters as springs or diffuse

plumes; and 3) direct atmospheric deposition (Figure 3).23

Nitrogen has always been delivered from the land to the

sea, and this transfer helps make coastal waters productive.

However, increases in N that can be used by primary

producers (bioavailable N) arising from increases in human

activities pose a threat to healthy coastal systems (see

shaded box, on this page). For example, an estimated 

37 percent of the world’s population currently lives within

62 miles of the coastline, and we can expect 75 percent

of the U.S. population to live within 47 miles of the

coastline by the year 2010.24, 25 Increased coastal populations

with their residential, commercial, industrial, and agricultural

activities have increased the delivery of anthropogenic, or

human-derived, N and P to estuaries via point and nonpoint

sources of wastewater and fertilizer. Air pollution from

industry and cars also contributes N to coastal systems via

direct deposition into the sea or via deposition to land and

subsequent transport by groundwater or surface runoff.26

The pressure on coastal waters in states such as Florida

is increased by our country’s agricultural practices. A

majority of crop production in the United States occurs in

the inland, midwestern states, with food being transported

to people in coastal states. This translocation means that

coastal populations import N in the form of food from

inland regions and export N in the form of waste to coastal

6

HOW HAVE WE AFFECTED THE AVAILABILITY OF

NITROGEN?

Over the past century, human activities have more than

doubled the rate at which atmospheric N2 or organicallybound N is converted to biologically available forms 

(Table 1). The transfer of atmospheric N has increased due

to 1) increased cultivation of nitrogen-fixing crops such as

peas, alfalfa, and soybeans, and 2) production of artificial

fertilizers. The technology for the industrial production of

artificial fertilizers was developed in Germany during World

War I, after Fritz Haber synthesized the base for them,

NH3, by combining N2 and hydrogen gas (H2) at high

temperature and pressure. We have increased the transfer of

organically-bound N by 1) burning fossil fuels, such as coal

and oil, and 2) burning or clearing land.

Table 1. Global nitrogen fixation in terrestrial environments.

Data are summarized from Vitousek et al. (1997).23

Input New nitrogen

(million metric tons per year)

Pre-1900s

bacterial fixation 90–140

lightning <10

Total 100–150

Post-1900s

bacterial fixation 90–140

lightning <10

cultivation of N-fixing crops 40

fertilizer production 80

burning fossil fuels >20

burning or clearing existing land 70

Total 310–360
' Preserve wetland buffers or green space and submerged

aquatic vegetation associated with coastlines, rivers,

and streams. Important “buffer” habitats include salt

marshes and mangroves. Plants in these systems

remove N and P as they grow. In addition, wetland

sediments are good sites for “denitrification”, a

process in which bacteria convert nitrate (NO3, a

biologically available form of nitrogen) into nitrogen

gas (N2) that enters the atmosphere and becomes

less available to coastal primary producers. Efforts

should also be made to preserve submerged vegetation,

such as seagrasses, because this vegetation also

removes nutrients. For example, people should

avoid direct removal of submerged vegetation by

dredging or raking, and they can minimize indirect

loss due to shading by building docks at a proper

height, orienting them north–south rather than

east–west, and spacing their boards.27

' Limit the use of fertilizers on residential and commercial

lawns and landscaping. When fertilizing, it is

important to minimize quantities and avoid

fertilizing before heavy rains. Storm water runoff

can transport fertilizer intended for yards directly to

coastal waters. A University of Florida extension

program, Florida Yards and Neighborhoods, provides

information to homeowners on environmentally

friendly landscaping that reduces storm water runoff,

decreases nonpoint source pollution, conserves water,

enhances wildlife habitat, and creates attractive

landscapes (see the web site listed below for further

information).

' Manage storm water runoff. Diverting runoff to

retention ponds or other temporary storage areas

minimizes direct input of nutrients to coastal waters.

Minimizing the extent of impervious surfaces while

maximizing the cover of natural vegetation also

reduces the amount of storm water runoff delivered

to coastal waters.

' Use better septic systems. Repairing old or leaking

septic systems or replacing them with more efficient

systems will help keep nutrients from reaching

groundwater or runoff. For example, denitrifying

systems rely on the natural microbial process of

“denitrification” to convert nitrate (NO3), which

can enter groundwater and move to coastal waters,

into nitrogen gas (N2) that is instead released to the

atmosphere.

7

systems. Overall, coastal systems receive a disproportionately

high load of nitrogen generated by the activities of people.

CAN T WE JUST ADD THE RIGHT

AMOUNT OF NITROGEN?

Scientists and environmental managers are attempting to

predict the level of N loading that a system can

accommodate. The concept of assimilative capacity or total

maximum daily load (TMDL) refers to this threshold.

Unfortunately, the nutrient load that causes undesirable

changes in coastal ecosystems, the threshold loading, is not

a simple thing to predict. Uncertainty arises from many

causes, including the complex and interactive cycles of N and

other nutrients, geological variation among sites, seasonal

variations in rainfall and sunlight, and the influence of

isolated events. For example, a system may exceed its

assimilative capacity when unusually large rainfalls deliver

high pulses of nutrients. Once the system has undergone a

change, it may not readily revert back to its former state.

Scientists and managers are also protecting our coastal

systems by monitoring their status and adjusting

management efforts accordingly. Monitoring often involves

measurements of nutrient concentrations in the water

column, but these concentrations change rapidly and vary

from place to place. Such variation makes it difficult to

accurately identify long-term increases. As a “safety net”,

some monitoring includes bioindicators and bioassays that

focus on changes in natural vegetation, changes in growth

rates, or changes in the type of N found in plants. The

hope is that these “indicators” will integrate short-term

pulses to provide an improved view of long-term trends.

WHAT CAN WE DO?

First and foremost, we can limit nutrient inputs tocoastal waters. Examples of actions that might decrease

nutrient loading to coastal waters include:

' Limit urban development, especially along shorelines.

Increases in development result in increased nutrient

loads via many pathways. For example, more

development and more people often mean that

coastal waters will receive more nutrients from septic

systems, wastewater treatment plants, or fertilized

lawns and landscaping. Development increases the

amount of “impervious surfaces” (such as roads,

driveways, or roofs) that generate nutrient-rich,

storm water runoff, and it also diminishes forests

and natural “green spaces” that slow runoff and

remove nutrients.
REFERENCES

1) Florida Coastal Management Program. 2000. Florida 

assessment of coastal trends. Florida Department of 

Community Affairs, Tallahassee, FL. pp. 1–148.

2) Florida Coastal Management Program. 1996. Florida State 

of the Coast Report, Preparing for a Sustainable Future. 

Florida Department of Community Affairs. Tallahassee, 

Florida. 28 pp.

3) Ryther, J.H. 1969. Photosynthesis and fish production in 

the sea. Science 166: 72–76.

4) Humphreys, J., S. Franz, B. Seaman, and J. Potter. 1993. 

Florida’s estuaries: a citizen’s guide to coastal living and 

conservation. Florida Sea Grant Publication SGEB–23. 

Florida Sea Grant, Gainesville, Florida. 25 pp.

5) Department of Environmental Protection, Florida Marine 

Research Institute web site: www.myflorida.com/

environment/learn/waterprograms/preserves/habitats/

mangroves.html.

6) Short, F.T. and S. Wyllie-Echeverria. 1996. Natural and 

human-induced disturbance of seagrasses. Environmental 

Conservation 23: 17–27.

7) Sargent, F.J., T.J. Leary, D.W. Crewz, and C.R. Kruer. 1995.

Scarring of Florida’s seagrasses: assessment and management

options. FRMI Technical Report RT-1. Florida Marine 

Research Institute, St. Petersburg, Florida. 37 pp. plus 

appendices.

8) Kemp, W.M., R.R. Twilley, J.C. Stevenson, W.R. Boynton, 

and J.C. Means. 1983. The decline of submerged vascular 

plants in upper Chesapeake Bay: Summary of results 

concerning possible causes. Marine Technology Society 

Journal 17: 78–89.

9) Group of Experts on the Scientific Aspects of Marine 

Pollution (GESAMP). 1990. The state of the marine 

environment. Blackwell Scientific Publications, Oxford. 

146 pp.

10) Short, F.T., D.M. Burdick, J.S. Wolf, and G.E. Jones. 1993.

Eelgrass in estuarine research reserves along the East Coast, 

U.S.A., Part I: Declines from pollution and disease and Part

II: Management of eelgrass meadows. National Oceanic 

and Atmospheric Administration, Coastal Ocean Program 

Publication, Rockville, Maryland. pp. 1–83, M1–M24.

' Improve sewage treatment plants. Different levels of

wastewater treatment result in different levels of

nutrient removal. Tertiary treatment results in the

most complete removal of nutrients. Improved

wastewater treatment can dramatically affect coastal

ecosystems. For example, two decades ago, seagrass

coverage in Tampa Bay was less than 30 percent of

historical levels. The loss was largely attributed to

nutrient loading. In the 1980s, improving treatment

of inputs from domestic and industrial point sources

created a 50 percent reduction in N loading. Water

quality in Tampa Bay has steadily improved, and, as

a result, coverage of seagrass has expanded by about

12 percent.28

' Support efforts to improve our knowledge. We can all

support research and monitoring that will supply

information that is critical to future improvements.

In short, we can strive to know more so that we can

make informed decisions.

Understanding the response of coastal primary producers to nutrient loading, the interactions among these producers, and the indirect effects of changes in these producers on other elements of coastal systems is crucial for

preventing loss and damage in coastal environments.

Preventing loss and damage is the most effective form of

management, because restoration of coastal habitats will be

far more costly and difficult if not impossible.29–31

At this time, it is difficult to accurately predict the

amount of nutrients that can be safely added to coastal

waters. Small-scale experiments have shown the existence of

links between nutrient supply, algal production, and loss of

seagrass habitat.16, 17, 32–36 However, numerical relationships

that specify the exact nutrient load resulting in undesirable

responses at the estuary scale are only available for a few

systems around the world. We need to conduct large-scale

experiments and undertake monitoring to validate

extrapolations and predictions made from small-scale

experiments and to accurately estimate the rate at which

nutrients are being added to Florida’s coastal waters.

Monitoring not only helps us understand the interactions

between human activities and coastal systems at larger scales,

it also gives us early warnings of problems.

Scientists, managers, and community members need to

work together to develop research initiatives and monitoring

programs that detect and predict small, relevant changes

caused by increased nutrient loads. Such experimental and

observational research would allow us to further understand

the relationship between nutrient loading and changes to

coastal habitats. This understanding can be used to formulate

effective, but not unnecessarily restrictive, policies for

managing human activities.

8
9

11) National Research Council. 1994. Priorities for Coastal 

Ecosystem Science. National Academy Press. Washington, 

D.C. 118 pp.

12) Valiela, I., J. McClelland, J. Hauxwell, P.J. Behr, D. Hersh, 

and K. Foreman. 1997. Macroalgal blooms in shallow 

estuaries: Controls and ecophysiological and ecosystem 

consequences. Limnology and Oceanography 42: 1105–1118.

13) United States Geological Survey. 1999. The quality of our 

nation’s waters – nutrients and pesticides. United States 

Geological Survey Circular 1225. pp. 1–82.

14) Hauxwell, J., J. Cebrián, C. Furlong, and I. Valiela. 2001. 

Macroalgal canopies contribute to eelgrass (Zostera marina)

decline in temperate estuarine ecosystems. Ecology 82: 

1007–1022.

15) Duarte, C. 1995. Submerged aquatic vegetation in relation 

to different nutrient regimes. Ophelia 41: 87–112.

16) Short, F.T., D.M. Burdick, and J.E. Kaldy III. 1995. 

Mesocosm experiments quantify the effects of 

eutrophication on eelgrass, Zostera marina. Limnology and 

Oceanography 40: 740–749.

17) Taylor, D., S. Nixon, S. Granger, and B. Buckley. 1995. 

Nutrient limitation and the eutrophication of coastal 

lagoons. Marine Ecology Progress Series 127: 235–344.

18) Hauxwell, J., J. McClelland, P.J. Behr, and I. Valiela. 1998. 

Relative importance of grazing and nutrient controls of 

macroalgal biomass in three temperate shallow estuaries. 

Estuaries 21: 347–360.

19) Weiss, E. 2001. The effect of N loading on the growth rates

of quahogs and softshell clams through changes in food 

supply. Boston University, M.A. Thesis. 52 pp.

20) Rabalais, N.N., W.J. Wiseman, Jr., R.E. Turner, D. Justic, 

B.K. Sen Gupta, and O. Dortch. 1996. Nutrient changes 

in the Mississippi River and system responses on the 

adjacent continental shelf. Estuaries 19: 386–407.

21) Malakoff, D. 1998. Death by suffocation in the Gulf of 

Mexico. Science 281: 190–192.

22) Ferber, D. 2001. Keeping the stygian waters at bay. Science 

291: 968–973.

23) Vitousek, P.M., J. Aber, R.W. Howarth, G.E. Likens, P.A. 

Matson, D.W. Schindler, W.H. Schlesinger, and G.D. 

Tilman. 1997. Human alteration of the global nitrogen 

cycle: causes and consequences. Ecological Applications 

7: 737–750.

24) Williams, S.J., D. Dodd, and K.K. Gohm. 1991. Coasts in 

crisis. United States Geological Survey Circulation 1075. 

32 pp.

25) Cohen, J.E., C. Small, A. Mellinger, J. Gallup, and 

J.D. Sachs. 1997. Estimates of coastal populations. 

Science 278: 1211.

26) Corbett, R.D., W.C. Burnett, and J.P. Chanton. 2001. 

Submarine groundwater discharge: an unseen yet 

potentially important coastal phenomenon. Florida Sea 

Grant, Gainesville, Florida. 6 pp.

27) Burdick, D.M. and F.T. Short. 1998. Dock design with the 

environment in mind: minimizing dock impacts to eelgrass 

habitats (CD-ROM). New Hampshire Sea Grant, program 

number: UNHMP-V-SG-98-18. National Sea Grant 

Library number: NHU-C-98-001.

28) Johansson, J.O.R. and H.S. Greening. 2000. Seagrass 

restoration in Tampa Bay: a resource-based approach to 

estuarine management. pp. 279–293. In Bortone, S.A. 

(ed.), Seagrasses: Monitoring, Ecology, Physiology, and 

Management. CRC Press, New York.

29) Harrison, P.G. 1990. Variations in success of eelgrass 

transplants over a five-year period. Environmental 

Conservation 17: 157–163.

30) Davis, R.C. and F.T. Short. 1997. Restoring eelgrass, 

Zostera marina L., habitat using a new transplanting 

technique: the horizontal rhizome method. Aquatic Botany 

59: 1–15.

31) Davis, R.C., F.T. Short, and D.M. Burdick. 1998. 

Quantifying the effects of green crab damage to eelgrass 

transplants. Restoration Ecology 6: 297–302.

32) Twilley, R.R., W.M. Kemp, K.W. Staver, J.C. Stevenson, 

and W.R. Boynton. 1985. Nutrient enrichment of estuarine

communities. 1. Algal growth and effects on production of 

plants and associated communities. Marine Ecology 

Progress Series 23: 179–191.

33) Burkholder, J.M., H.B. Glasgow, Jr., J.E. Cooke. 1994. 

Comparative effects of water-column nitrate enrichment on

eelgrass Zostera marina, shoalgrass Halodule wrightii, and 

widgeongrass Ruppia maritima. Marine Ecology Progress 

Series 105: 121–138.

34) Neckles, H.A., R.L. Wetzel, and R.J. Orth. 1993. Relative 

effects of nutrient enrichment and grazing on 

epiphyte-macrophyte (Zostera marina L.) dynamics 

Oecologia 93: 285–295.

35) Taylor, D.I., S.W. Nixon, S.L. Granger, B.A. Buckley, 

J.P. McMahon, and H. J. Lin. 1995. Responses of coastal 

lagoon plant communities to different forms of nutrient

enrichment – a mesocosm experiment. Aquatic Botany 

52: 19–34.

36) Moore, K.A. and R.L. Wetzel. 2000. Seasonal variations in 

eelgrass (Zostera marina L.) response to nutrient 

enrichment and reduced light availability in experimental 

ecosystems. Journal of Experimental Marine Biology and 

Ecology 244: 1–28.
10

WEB SITES

• State of Florida http://www.myflorida.com

• National Sea Grant http://www.nsgo.seagrant.org

• Florida Sea Grant http://www.flseagrant.org

• Florida Yards and Neighborhoods

http://hort.ufl.edu/fyn

• Florida NOAA/NERR

Apalachicola (Apalachicola, FL) NOAA 

National Estuarine Research Reserve 

http://inlet.geol.sc.edu/APA/

Rookery Bay (Naples, FL) NOAA National 

Estuarine Research Reserve 

http://inlet.geol.sc.edu/RKB/

• Florida EPA National Estuary Program

Indian River Lagoon 

http://www.epa.gov/owow/estuaries/irl.htm

Tampa Bay 

http://www.epa.gov/owow/estuaries/tampa.htm

Sarasota Bay 

http://www.epa.gov/owow/estuaries/sb.htm

Charlotte Harbor 

http://www.epa.gov/owow/estuaries/ch.htm

• Florida Water Management Districts

St. Johns River Water Management District 

http://sjr.state.fl.us

Southwest Florida Water Management District 

http://www.swfwmd.state.fl.us

South Florida Water Management District 

http://www.sfwmd.gov

Northwest Florida Water Management District 

http://sun6.dms.state.fl.us/nwfwmd

Suwannee River Water Management District 

http://www.srwmd.state.fl.us

• Florida Center for Environmental Studies 

http://www.ces.fau.edu/library/marinesgrass/ 

index.html

• Florida Oceanographic Society 

http://www.fosusa.org/environ/seagrass1.htm

• University of Hawaii (seagrass pictures)

http://www.botany.hawaii.edu/seagrass/pgallery.htm

BIBLIOGRAPHY

SUMMARY JOURNAL ARTICLES & REPORTS

• Group of Experts on the Scientific Aspects of Marine 

Pollution (GESAMP). 1990. The state of the marine 

environment. Blackwell Scientific Publications, Oxford.

• U.S. Geological Survey. 1999. The quality of our nation’s 

waters - nutrients and pesticides. U.S. Geological Survey 

Circular 1225. pp. 1–82. On-line at: 

http://water.usgs.gov/pubs/circ/circ1225

• Vitousek, P.M., J. Aber, R.W. Howarth, G.E. Likens, 

P.A. Matson, D.W. Schindler, W.H. Schlesinger, and 

G.D. Tilman. 1997. Human alteration of the global nitrogen

cycle: causes and consequences. Issues in Ecology 1: 1–15.

Available from: Public Affairs Office, Ecological Society of

America, 2010 Massachusetts Avenue NW, Suite 400,

Washington, DC 20036; esahq@esa.org; (202) 833-8773;

on-line at: http://esa.sdsc.edu

• Carpenter, S., N.F. Caraco, D.L. Correll, R.W. Howarth,

A.N. Sharpley, and V.H. Smith. 1998. Non-point pollution of surface waters with phosphorus and nitrogen. Issues

in Ecology 3: 1–12. Available from: Public Affairs Office,

Ecological Society of America, 2010 Massachusetts Avenue

NW, Suite 400, Washington, DC 20036; esahq@esa.org;

(202) 833-8773; on-line at: http://esa.sdsc.edu

BOOKS

• National Research Council. 1994. Priorities for Coastal

Ecosystem Science. National Academy Press. Washington,

D.C. ISBN: 0-309-05096-0. On line at:

http://www.nap.edu/books/0309050960/html/index.html

• Howarth, R.W. 1993. The role of nutrients in coastal 

waters. In: Managing Wastewater in Coastal Urban Areas. 

Report from the National Research Council Committee on

Wastewater Management for Coastal Urban Areas. 

National Academy Press. ISBN: 0-309-04826-5. On line 

at: http://lab.nap.edu/books/0309048265/html/index.html

• Nixon, S.W. and M.E.Q. Pilson. 1983. Nitrogen in estuarine

and coastal marine ecosystems. In: Nitrogen in the Marine 

Environment, E.J. Carpenter and D.G. Capone, eds. 

Academic Press. New York. 900 pp. ISBN: 0-121-60280-X.

Science Serving 

Florida’s Coast

Florida Sea Grant College Program

University of Florida

PO Box 110409 

Gainesville, FL 32611-0409

(352) 392-5870

www.flseagrant.org

October 2001

Reviewed October 2008